Most U.S. residential and commercial buildings are equipped with central forced air heating and/or cooling systems. Indoor air is drawn into the system by the central blower, pumped through the central unit where it is heated or cooled, then redistributed throughout the building. A mechanical air filter is positioned upstream of the central blower to filter air which is to be heated or cooled and thence distributed. The vast majority of these filters are composed of a coarse filter media such as glass or polyester fiber, supported in a paperboard frame and slidably installed within a channel formed in the central unit blower compartment or return air duct work. Such filters are considered "disposable", since the composition and construction of the filters makes it economically unattractive to attempt to clean and reuse the filter.
The major fault with disposable or "non-permanent" filters lies in the fact that the requisite high porosity of the filter causes the efficiency of the filter to decrease radically with respect to airborne particle size below 100 microns in diameter, so as to become virtually ineffective on particles below 10 microns in diameter.
In order to obtain a more efficient filter, the principle electrostatically charged filtering media has been utilized for many years. Conventionally, a high voltage is applied to a metallic grid which is located adjacent a layer of dielectric filter media. A metallic grill is located on the opposing side of the filter media such that an electrostatic field is produced between the charged grid and the grounded grill. The electrostatic field thus created polarizes the filter media as well as any particles in the air passed through the filter. This polarization greatly increases the tendency of airborne particulate to adhere to the surfaces of the filter media, thereby significantly increasing the overall efficiency of the filtering process.
While electrostatic filtering systems have been known for many years, they still suffer drawbacks. Because electrostatic filters may be cleaned and reused, they are commonly described as "permanent" filters. Prior art permanent electrostatic filters are commonly manufactured with a collecting cell which is removably installed in the central forced air system, and have a separate power supply electrically connected to the collecting cell. Thus, a length of high voltage electrical line must extend from the power supply to the collecting cell. Such an electrical line is necessarily both relatively cumbersome and permanently attached to the collecting cell thereby complicating the installation, removal, and cleaning of the collecting cell.
Another drawback of prior art electrostatic filters relates to the methods utilized in cleaning such filters. The simplest and most effective method for cleaning permanent electrostatic filters is the utilization of a common household automatic dishwasher. This method of cleaning, however, is not available to the majority of the owners of permanent filters, because approximately two-thirds of all permanent filters are 24 or more inches in length. Since the standard domestic dishwasher has dimensions which would accept filters of only about 20 inches in length, the owners of filters of a greater length are excluded from this convenient cleaning method. Rather, they must resort to manual cleaning of the filters by spraying or saturating the filter with water in a large container, sink, or the like.
As described above, cleaning conventional permanent electronic air filters involves saturating the collecting cell in water. If the air filter is reinstalled in the furnace and energized before the collecting cell has dried, high voltage arcing will occur through the filter media between the high voltage grid and the grounded grills. While such arcing is not necessarily damaging, it creates a loud annoying "popping" sound which can continue for an appreciable length of time. Prior to the applicant's invention, the "solution" to this problem generally entailed leaving the saturated unit deactivated for a length of time to permit adequate drying of the collecting cell. However, this also poses problems, since the consumer could easily forget to reactivate the unit, thereby compromising the effectiveness of the unit. In any event, the owner is required to remember to activate the unit after an appropriate period of time.
Another drawback of some electronic air filters is in the inability of the consumer to easily monitor the performance and operation of the filter. Since the electronic filter is normally silent the consumer may only visually check the position of the on/off switch, or pilot light for the unit, if any exists, to determine whether the unit is activated. The consumer cannot conveniently and easily check the performance or normal operating parameters of the collecting cell.
Finally, many of the prior art electronic air cleaners require a large amount of labor and high degree of expertise to install the mechanism within the central forced air system.
It is therefore a general object of the present invention to provide an improved electronic air filter.
Another object of the present invention is to provide an electronic air filter with a waterproof high voltage power supply mounted integrally within the filter frame such that only a low voltage line need extend from the filter frame to a household power supply.
A further object of the present invention is to provide an electronic air filter which may be folded to fit within the dimensions of a standard domestic automatic dishwasher.
Still another object of the present invention is to provide an electronic air filter with electrical shunts which will prevent arcing as the components of the collecting cell dry after cleaning.
Yet a further object is to provide an electronic air filter with performance indicator apparatus which permits the consumer to monitor the operation and performance of the filter.
Still another object of the present invention is to provide an electronic air filter which is simply and quickly installed in a central heating/cooling system, without requiring highly skilled technicians.
These and other objects of the present invention will be apparent to those skilled in the art.